KR20140146042A - Radicals and their use as paramagnetic agents in a dynamic nuclear polarisation process - Google Patents

Abstract

The present invention relates to a novel radical, its use as paramagnetic material in a dynamic nuclear polarization method, and a dynamic nuclear polarization method of a compound containing a carboxyl group.

Description

≪ Desc / Clms Page number 1 > RADICALS AND THEIR USE AS PARAMAGNETIC AGENTS IN A DYNAMIC NUCLEAR POLARIZATION PROCESS IN ROCK AND DYNAMIC NUCLEAR POLARIZATION PROCESS.

The present invention relates to a novel radical, its use as paramagnetic material in a dynamic nuclear polarization method, and a dynamic nuclear polarization method of a compound containing a carboxyl group.

Magnetic resonance (MR) imaging (MRI) is particularly popular with physicians because it obtains images of the patient's body or parts thereof in a non-invasive manner and prevents patients and medical personnel from being exposed to potentially harmful radiation such as X- Imaging technology. Because of its high quality imaging, MRI is a preferred imaging technique for soft tissues and organs, which allows differentiation between normal and diseased tissues, such as tumors and lesions.

MR tumor imaging may be performed in the presence or absence of an MR contrast agent. In MR images taken without contrast media, tumors of about 1-2 cm in size and larger will appear to be fairly conspicuous. However, contrast-enhanced MRI can detect much smaller tissue changes, that is, much smaller tumors, and contrast-enhanced MR imaging is a powerful tool for early-stage tumor detection and detection of metastasis.

Several types of contrast agents have been used for MR tumor imaging. Gadolinium chelates such as water-soluble paramagnetic metal chelates, for example Omniscan (Omniscan; Amersham Health), are widely used as MR contrast agents. When administered as a vasculature, they are rapidly distributed into the extracellular space (i.e., blood and epilepsy) because of their small molecular weight. They are also removed relatively quickly from the body. Gadolinium chelates have been found to be particularly useful in increasing the detection rate of metastatic and small tumors and improving tumor classification, the latter being associated with central necrosis, and from peripheral edema or macroscopic involvement of lethal tumor tissue (See, for example, C. Claussen et al., Neuroradiology 1985; 27: 164-171).

On the other hand, blood pool MR contrast agents, such as superparamagnetic iron oxide particles, are retained in the long-term vasculature. They have not only been shown to enhance contrast in the liver, but have proven to be very useful in detecting capillary walls that are "leaking" from tumors as a result of capillary permeability abnormalities, such as angiogenesis.

Despite the apparently excellent properties of the contrast agent, there is a certain risk involved in their use. The paramagnetic metal chelate complexes generally have a consistently high stability, but toxic metal ions may be released in the body after administration. Also, this type of contrast agent exhibits poor specificity.

WO-A-99/35508 discloses a MR imaging method for a patient using a hyperpolarized solution of a high T ₁ material as an MRI contrast agent. The term " hyperpolarization "means enhancing the nuclear polarization of the NMR active nuclei present in the high T ₁ material, i.e., non-zero nuclear spin nuclei, preferably ¹³ C- or ¹⁵ N nuclei. When enhancing the nuclear polarization of the NMR active nuclei, the difference between the excitation and basal nuclear spin states of these nuclei is significantly increased, and thereby the MR signal intensity is amplified by a factor of more than 100. When using the highly polarized ¹³ C- and / or ¹⁵ N-enriched high T ₁ material, the natural abundance ratio of ¹³ C and / or ¹⁵ N would be negligible and would not be substantially interfered by the background signal, . A variety of high T ₁ materials are described which are suitable for use as a post-polarizing and subsequently MR contrast agent, and include, but are not limited to, non-endogenous and non-endogenous substrates such as acetate, pyruvate, oxalate or gluconate Endogenous compounds, sugars such as glucose or fructose, amino acids such as urea, amide, glutamate, glycine, cysteine or aspartate, vitamins such as nucleotides, ascorbic acid, penicillin derivatives and sulfonamides. Metabolic circuits such as fumaric acid and pyruvic acid, such as intermediates in citric acid circuits, are preferred contrast agents for imaging metabolism activity.

It has been a problem that the signal of the hyperpolarised contrast agent is attenuated by relaxation and dilution when administered into the body of a patient. Therefore, the T ₁ value of the contrast agent in a biological fluid (e.g., blood) should be long enough so that the material can be distributed in a highly-polarized state on the target site of the patient's body. Regardless of contrast agents with high T ₁ values, achieving a high level of polarization is highly desirable.

Several secularization techniques are disclosed in WO-A-99/35508, one of which is based on dynamic nuclear polarization (DNP), in which the polarization of the sample is influenced by paramagnetic compounds called so-called paramagnetic or DNP materials ) Technology. During the DNP process, energy is normally provided in the form of microwave radiation, which will initially excite paramagnetic materials. At the same time as it is attenuated to the ground state, the polarization is shifted from the non-paired electrons of the paramagnetic material to the NMR active nuclei of the sample. Generally, medium or high magnetic fields and very low temperatures are used in the DNP process, for example, DNP processes at liquid helium and magnetic fields of about 1 T or greater. Alternatively, any temperature that can achieve an intermediate magnetic field and sufficient polarization enhancement can be used. DNP technology is described, for example, in WO-A-98/58272 and WO-A-01/96895, which are incorporated herein by reference.

Paramagnetic materials play a significant role in the DNP process, and the choice has a major impact on the level of polarization achieved. A-99/35508, WO-A-88/10419, and WO-A-99/35508 disclose various paramagnetic materials - referred to as "OMRI contrast agents" Based or sulfur-based materials mentioned in WO-A-90/00904, WO-A-91/12024, WO-A-93/02711 or WO- ≪ / RTI > based organic glass radicals or magnetic particles.

The inventors have surprisingly found that the use of certain radicals as paramagnetic materials in dynamic nuclear polarization of compounds containing carboxyl groups results in a significantly higher level of polarization.

Accordingly, in one aspect, the present invention provides a method for the dynamic nuclear polarization of a compound comprising at least one carboxyl group, characterized in that a radical of formula (I) is used as a paramagnetic material in a dynamic nuclear polarization (DNP) ) Method.

(I)

Wherein,

M represents hydrogen or a monovalent cation;

R 1 is the same or different and represents a straight or branched C ₁ -C ₆ -alkyl group or a - (CH ₂ ) _n -X-R ₂ group; Wherein n is 1, 2 or 3, X is O or S, and R is a linear or branched C ₁ -C ₄ -alkyl group.

The method according to the invention leads to a high level of polarization in the compound to be polarized. Extra-polarization of compounds that play a role in the metabolism in the body of humans and animals other than humans is of great interest because it is important to obtain information about the metabolic status of tissues in vivo MR studies In other words they are potentially useful as imaging agents for in vivo MR imaging of metabolic activity. Information on the metabolic status of the tissue can be used, for example, to distinguish between healthy and tumor tissues, and thus a hyperpolarizing compound, which plays a role in the metabolic process, can be used as a potential imaging agent for in vivo MR tumor imaging .

Many compounds that play a predetermined role in the metabolism in the body of a human or non-human animal exhibit high chemical reactivity. The inventors have found that the radicals of formula (I) are particularly useful for the DNP of such compounds, since the radicals of formula (I) exhibit very low reactivity towards these types of compounds. It has also been found that intimate contact between the radical of formula (I) and the compound to be polarized induces an increase in the level of polarization. It has been found that the solubility of the radicals is considerably extended according to pH in the dissolution medium and that radicals of the formula (I) have good solubility in the pH range particularly useful for formulating this type of compound. Specifically, a compound that plays a predetermined role in the metabolic process mainly comprises at least one carboxyl group. The radicals of formula (I) have been found to be stable to compounds containing carboxyl groups and the radicals are readily soluble in a compound containing a carboxyl group or in a radical solution of formula (I), and the compound containing a carboxyl group is dissolved in a suitable solvent or solvent Can be easily prepared using a mixture.

In a preferred embodiment, a radical of formula (I) in which M represents hydrogen or a physiologically acceptable monovalent cation is used in the process according to the invention. The term "physiologically acceptable cation" refers to a cation that is acceptable to the living body of a human or non-human animal. Preferably, M represents hydrogen or an alkali cation, an ammonium ion or an organic amine ion such as meglumine. Most preferably, M represents hydrogen or sodium.

In a further preferred embodiment, the radical of the formula (I) in which R 1 is identical and more preferably a straight-chain or branched C ₁ -C ₄ -alkyl group, most preferably methyl, ethyl or isopropyl, Method.

In a further preferred embodiment of the, R1 is the same or different, preferably identical, and _{-CH 2 -OCH 3, -CH 2 -OC} 2 H 5, -CH 2 -CH 2 -OCH 3, -CH 2 -SCH in the _3, -CH ₂ -SC ₂ H ₅ or -CH ₂ -CH ₂ -SCH _3, most preferably from how the radical of the formula (I) represents a -CH ₂ -CH ₂ -OCH ₃ according to the invention do.

In a more preferred embodiment, M represents hydrogen or sodium, and R 1 is the same and represents -CH ₂ -CH ₂ -OCH ₃ .

The radicals used in the process of the present invention can be synthesized as detailed in WO-A-91/12024 and WO-A-96/39367. Briefly, radicals can be synthesized by reacting 3 molar equivalents of a metallized monomeric aryl compound with one molar equivalent of a suitably protected carboxylic acid derivative to form a trimeric intermediate. This intermediate is metallized and subsequently reacted with, for example, carbon dioxide to form tri-carboxyl trityl carbinol, which in a further step is treated with strong acid to produce the triarylmethyl cation. This cation is then reduced to form a stable trityl radical. For synthesis of a radical of formula (I) wherein M is hydrogen or sodium and R 1 is the same and -CH ₂ -CH ₂ -OCH ₃ , the following scheme and Example 1 can be used, respectively.

[Reaction Scheme 1]

[Reaction Scheme 2]

In a preferred embodiment of the method of the present invention, the compound comprising at least one carboxyl group is a compound which plays a role in the endogenous compound, more preferably in the metabolism in the body of an animal other than human or human.

Preferred compounds comprising at least one carboxyl group are, for example, acidic amino acids such as aspartic acid and glutamic acid, and these amino acids are involved in protein metabolism. Also preferred are acetic acid, acetoacetic acid and hydroxybutyric acid, which are involved in lipid metabolism. Other preferred compounds are lactic acid and pyruvic acid, which are involved in energy metabolism, and fumaric acid, succinic acid, citric acid and malic acid, which are citric acid circuit intermediates. Further preferred compounds are ascorbic acid and fatty acids, preferably palmitic acid and oleic acid.

The compound comprising at least one carboxyl group used in the method of the present invention is preferably an isotopically enriched compound wherein the isotope enrichment is carried out using a non-zero spin nucleus (MR active nucleus), preferably ¹⁵ N and / or ¹³ C , More preferably ¹³ C isotope enrichment. Isotopic enrichment may include selective enrichment of one or more sites or uniform enrichment of all sites within a compound molecule. Concentration can be achieved, for example, by chemical synthesis or biological labeling, both methods are well known in the art, and suitable methods can be selected differently depending on the compound to be isotopically enriched.

Preferably, the compound comprising at least one carboxyl group used in the method of the invention is enriched in isotope at only one position of the molecule, preferably at least 10%, more preferably at least 25% 75% or more, and most preferably 90% or more. Ideally, the concentration is 100%.

The optimal location for isotope enrichment in compounds containing at least one carboxyl group used in the method of the invention depends on the relaxation time of the MR active nucleus. Preferably, the compound is isotopically enriched at a position having a long T ₁ relaxation time. It is preferred that ¹³ C-enriched compounds enriched in a carboxyl-C-atom, a carbonyl-C-atom or a quaternary C-atom are used. If pyruvic acid is polarized according to the method of the present invention, C1- position ⁽¹³ C ₁ - pyruvate), C2- position ⁽¹³ C ₂ - pyruvate), C3- position ⁽¹³ C ₃ - pyruvate), C1- and C2 location ⁽¹³ C _{1, 2-pyruvate),} C1- and the C3- position ⁽¹³ C _{1, 3-pyruvate),} C2- and C3- position ⁽¹³ C _{2,3-pyruvate)} or C1-, C2- and C3- position ⁽¹³ C _{1, 2,3} - pyruvic acid) can be enriched in the isotope, and; The C1-position is preferred for ¹³ C isotopic enrichment.

Several methods for the synthesis of ¹³ C-pyruvic acid are known in the art. Briefly, Seebach et al., Journal of Organic Chemistry 40 (2), 1975, 231-237, discloses that S, S-acetals such as 1,3-dithiane or 2- Described is the synthetic route that depends on the protection and activation of the 3-dithiane carbonyl-containing starting material. The dithiane is metallized and reacts with methyl-containing compounds and / or ¹³ CO ₂ . ¹³ C ₁ -pyruvic acid, ¹³ C ₂ -pyruvic acid or ¹³ C _{1 , 2} -pyruvic acid can be obtained by using a suitable isotopically enriched ¹³ C-component as outlined in this document. Another synthetic route is from acetic acid, which is first converted to acetyl bromide and then reacted with Cu ¹³ CN. The thus obtained nitrile is converted to pyruvic acid via an amide (see, for example, SH Anker et al., J. Biol. Chem. 176 (1948), 1333 or JE Thirkettle, Chem Commun. , 1025]). In addition, ¹³ C-pyruvic acid can be obtained by adding both to commercially available sodium ¹³ C-pyruvate by, for example, the method described in U.S. Patent No. 6,232,497.

In a further preferred embodiment the compound comprising at least one carboxyl group used in the process of the present invention is a liquid at room temperature (for example pyruvic acid or lactic acid) and the radical of formula (I) is selected to be soluble in the liquid compound . This will form a concentrated compound / radical solution without the need for additional solvent to be present in the mixture. In a most preferred embodiment of the process of the present invention, the compound comprising at least one carboxyl group is ¹³ C-pyruvic acid, preferably ¹³ C ₁ -pyruvic acid, the radical of formula (I) And is a radical representing -CH ₂ -CH ₂ -OCH ₃ .

When the compound comprising at least one carboxyl group used in the process of the present invention is a solid at room temperature it can be melted and then the molten compound is mixed with the radical of formula (I) to dissolve the radical in the molten compound have. Subsequently, the solution is allowed to cool and / or freeze, preferably in such a manner as to prevent the compound to be polarized from crystallizing. Cooling / freezing can be accomplished by methods known in the art, for example, by freezing the solution in liquid nitrogen, or by allowing the liquid helium to freeze the solution and simply placing it on the DNP polarizer. In another embodiment, the solid compound comprising at least one carboxyl group may be dissolved in a suitable solvent or solvent mixture, preferably a good glass former, in a solvent that prevents it from crystallizing as it is cooled / frozen. Suitable glass formers are, for example, glycerol, propanediol or glycol. The dissolved compound is then mixed with the radical of formula (I) and the solution is cooled and / or frozen for the DNP process. Intimate mixing may be further facilitated by several means known in the art, such as stirring, vortexing or sonication.

DNP technology is described, for example, in WO-A-98/58272 and WO-A-01/96895, both of which are incorporated herein by reference. Generally, medium or high magnetic fields and very low temperatures are used in the DNP process, such as liquid helium, and DNP processes at a magnetic field of about 1 T or greater. Alternatively, any temperature that achieves an intermediate magnetic field and sufficient polarization enhancement can be used. In a preferred embodiment, the DNP process is performed in liquid helium and a magnetic field of about 1 T or greater. Suitable polarizing units are described, for example, in WO-A-02/37132. In a preferred embodiment, the polarization unit comprises a microwave chamber connected by a waveguide to a microwave source in a central bore surrounded by a chrysostat and a polarization means, for example a magnetic field generating means (e.g. a superconducting magnet) . The bore extends vertically down to a level of region P near the superconducting magnet with a sufficiently high magnetic field strength, for example 1 to 25 T, to cause the polarization of the ¹³ C nucleus. The sample bore is preferably sealable and can be evacuated to a low pressure, for example, a pressure of 1 mbar or less. A means for introducing a sample (i.e., a frozen compound / radical mixture), such as a removable sample transport tube, may be contained within the bore, which can be inserted down into the microwave chamber at the top of the bore. Region P is cooled to a temperature low enough to cause polarization by liquid helium, preferably from 0.1 to 100 K, more preferably from 0.5 to 10 K, most preferably from 1 to 5 K. The sample introducing means is preferably sealed in any suitable manner at the upper end to retain the partial vacuum at the bore. A sample-holding vessel, e.g. a sample-holding cup, may be removably mounted within the lower end of the sample introduction means. The sample-holding vessel is preferably made of a lightweight material, such as KeIF (polychlorotrifluoroethylene) or PEEK (polyetheretherketone), having low specific heat capacity and good cryogenic properties, . ≪ / RTI >

The sample is immersed in liquid helium, preferably at 200 mW, into a sample-holding vessel which is irradiated with microwaves at a frequency of about 94 GHz. The level of polarization can be monitored, for example, by obtaining a solid state ¹³ C- and / or ¹⁵ N-NMR signal of the sample that depends on the compound to be polarized during microwave radiation. In general, the saturation curve is obtained by plotting the NMR signal versus time. Thus, it can be determined when the optimal polarization level is reached.

When the compound polarized according to the method of the present invention is used as an MR imaging material, it is preferably dissolved in a physiologically acceptable aqueous carrier such as a buffer, for example, a suitable solvent after the DNP process, -02 / 37132, or is converted into a liquid hyperpolarised compound from a solid hyperpolarised compound by melting, for example, as described in WO-A-02/36005.

In addition, radicals and / or reaction products thereof may be removed from the liquid hypersensitive compound. Methods that can be used to partially, substantially or completely remove radicals and / or reaction products thereof are well known in the art. Generally, the applicable methods depend on the nature of the radical and / or the reaction product thereof. When dissolving the solid hyperpolarised compound, the radical can be precipitated, which can be easily separated from the liquid by filtration. If precipitation does not occur, the radical may be removed by chromatographic separation techniques, for example by liquid phase chromatography, for example reverse or normal phase chromatography, or ion exchange chromatography, or extraction.

Since the radical of formula (I) has a characteristic UV / visible light absorption spectrum, UV / visible light absorption measurements can be used in a way that confirms that it is present in the liquid after removal. To obtain a quantitative result, i. E. The concentration of radicals present in the liquid, the optical spectrometer can be adjusted in such a way that the absorption of the liquid sample in a particular wavelength form yields a corresponding radical concentration in the sample. Removal of the radicals and / or the reaction products thereof is particularly preferred when the liquid hyperpolarized compound is used as a contrast agent for in vivo MR imaging of a human or non-human animal's body.

Another aspect of the invention is a novel radical of formula (I)

(I)

Wherein,

M represents hydrogen or a monovalent cation;

R1 are the same or different, - (CH _{2) n} represents an -X-R2;

Wherein n is 1, 2 or 3,

X is O or S,

R2 is a straight or branched C ₁ -C ₄ -alkyl group.

Preferred radicals of formula (I) are radicals in which M represents hydrogen or a physiologically acceptable monovalent cation, preferably an alkali cation, an ammonium ion or an organic amine ion. Additionally, as the preferred radical of formula (I), and R1 are the _{same, -CH 2 -OCH 3, -CH 2} -OC 2 H 5, -CH 2 -CH 2 -OCH 3, -CH 2 -SCH 3, -CH ₂ -SC ₂ H _5, or the -CH ₂ -CH ₂ -SCH _3, most preferably a radical representing a -CH ₂ -CH ₂ -OCH _3. The most preferred radicals of the formula (I) are radicals in which M represents hydrogen or a physiologically acceptable monovalent cation, preferably sodium, and R 1 is the same and represents -CH ₂ -CH ₂ -OCH ₃ .

Another aspect of the invention is a composition comprising a compound comprising at least one carboxyl group and a novel radical of the formula (I)

(I)

Wherein,

M represents hydrogen or a monovalent cation;

R1 is the same or different and each is - (CH _{2) n} represents an -X-R2;

Wherein n is 1, 2 or 3,

X is O or S,

R2 is a straight or branched C ₁ -C ₄ -alkyl group.

The inventors have surprisingly found that the use of certain radicals as paramagnetic materials in dynamic nuclear polarization of compounds containing carboxyl groups results in a significantly higher level of polarization.

Example  1: Tris (8- Carboxy -2,2,6,6- ( Tetra (methoxyethyl) benzoate - [1,2,4,5 '] bis- (1, 3) Dithiol Yl) methyl  Synthesis of sodium salt

Synthesis of tris (8-carboxy-2,2,6,6- (tetra (hydroxyethyl) benzo [1,2-4,5 '] bistriazole synthesized according to Example 7 of WO-A1-98 / 39277 (1, 3) -dithiol-4-yl) methyl sodium salt was suspended in 280 ml of dimethylacetamide under an argon atmosphere. Sodium hydride (2.75 g) followed by methyl iodide (5.2 ml ) Was added and the slightly exothermic reaction was allowed to proceed for 60 minutes in a water bath at 34 DEG C. The addition of sodium hydride and methyl iodide was repeated twice with the same amount of compound respectively and after the final addition the mixture was stirred at room temperature After stirring for 68 hours, it was poured into 500 ml of water. The pH was adjusted to> 13 by addition of 40 ml of 1 M NaOH (aq) and the mixture was stirred at ambient temperature for 15 hours to hydrolyze the methyl ester formed The mixture was then acidified to pH ~ 2 using 50 ml of 2 M HCl (aq.) And extracted three times with ethyl acetate The combined organic phases were dried over Na ₂ SO ₄ and evaporated to dryness. The crude product (24 g) was purified by HPLC for purification using acetonitrile / water as eluent was. evaporation of the collected fractions to remove acetonitrile. extraction of the remaining water with ethyl acetate, dried organic layer over Na ₂ SO _4, evaporated to dryness. water was added (200 ml) to the residue and , 0.1 M NaOH (aq) was carefully added to adjust the pH to 7, and the residue slowly dissolved during this process. After neutralization, the aqueous solution was freeze-dried.

Example  2: ¹³ C- Pyruvic acid  And Example  1 of Radical  using Super-polarized ¹³ C- Pyruvate  Produce

¹³ C ₁ - pyruvic acid by dissolving 5.0 mg of the radical of Example 1 in the (164 ㎕) to prepare a 20 mM solution. The sample was homogeneously mixed and an aliquot (41 mg) of the solution was placed in a sample cup and inserted into the DNP polarizer.

The samples were polarized under DNP conditions at 1.2 K of a 3.35 T magnetic field with emission of microwave (93.950 GHz). After 2 hours, the polarization was stopped and the sample was dissolved in an aqueous solution of sodium hydroxide and tris (hydroxymethyl) -aminomethane (Tris) using a dissolution apparatus according to WO-A-02/37132 ≪ / RTI _> sodium chloride < RTI ID = 0.0 > ¹³ C < / RTI > The dissolved sample was analyzed rapidly by < ¹³ > C-NMR to evaluate the polarization and obtain 19.0% ¹³ C polarization.

Example  3: ¹³ C- Pyruvic acid  And Example  1 of Radical  using Super-polarized ¹³ C- Pyruvate  Produce

^A 15 mM solution was prepared by dissolving the radical of Example 1 (209.1 mg) in a mixture of ¹³ C ₁ -pyruvic acid (553 mg) and unlabeled pyruvic acid (10.505 g). The sample was homogeneously mixed and an aliquot of the solution (2.015 g) was placed in a sample cup and inserted into a DNP polarizer.

The samples were polarized under DNP conditions at 1.2 K of a 3.35 T magnetic field with emission of microwave (93.950 GHz). After 4 hours, the polarization was stopped and the sample was dissolved in an aqueous solution of sodium hydroxide and tris (hydroxymethyl) aminomethane (Tris) using a dissolution apparatus according to WO-A-02/37132 to give 100 mM tris A neutral solution of hyperpolarised sodium ¹³ C ₁ -pyruvate with a total pyruvate concentration of 0.5 M in the buffer was produced. In succession to the dissolution apparatus, a chromatography column was connected. The column consists of a cartridge (D = 38 mm; h = 10 mm) containing a hydrophobic packing material (Bondesil -C18, 40UM part no. 12213012) supplied by Varian. The dissolved sample is passed through a column that selectively adsorbs the radical. The filtered solution was analyzed rapidly by < ¹³ > C-NMR to evaluate the polarization and obtain 16.5% ¹³ C polarization. The residual radical concentration was subsequently analyzed with a UV spectrophotometer at 469 nm and the detection limit was determined to be less than 0.1 [mu] M.

Claims (7)

A composition for dynamic nuclear polarization of a compound comprising at least one carboxyl group, wherein the composition comprises a radical of formula (I).
(I)

Wherein,
M represents hydrogen or one equivalent of cation;
R1 is the same or different and each is - (CH _{2) n} represents an -X-R2;
Wherein n is 1, 2 or 3,
X is O or S,
R2 is a straight or branched C ₁ -C ₄ -alkyl group. 2. The composition of claim 1, wherein M represents hydrogen or a physiologically acceptable monovalent cation. The composition of claim 1, wherein M represents an alkali cation, an ammonium ion or an organic amine ion. The method of claim 1, wherein, R1 is the same and _{-CH 2 -OCH 3, -CH 2 -OC} 2 H 5, -CH 2 -CH 2 -OCH 3, -CH 2 -SCH 3, -CH 2 -SC 2 H ₅ or -CH ₂ composition will represent -CH ₂ -SCH _3. According to claim 1, wherein R1 is the same and will represent the -CH ₂ -CH ₂ -OCH ₃ composition. The method of claim 1 wherein M is hydrogen to the first acceptable or physiologically represents a cation, R1 is the same and represents the -CH ₂ -CH ₂ -OCH ₃ composition. The composition of claim 1, wherein the monovalent cation is a sodium cation.